The damaged expansion joints and pads around the bearings of the Howrah bridge need to be replaced, authorities of the Calcutta Port Trust, which maintains the 80-year-old structure, have written to police.
“We have appealed to police to allow a partial traffic block on the bridge for the upkeep. We want to start work next week,” said an official of the port trust.
Senior officers of Calcutta police said the repair team can work from 11pm till 4am, when portions of one of the two flanks can be barricaded.
“We have said the team can work only at night and only a part of one of the two flanks can be closed. The entire bridge cannot be closed to traffic,” a police officer said.
“Port trust officials have said they need close to eight months to complete the repairs in phases. We have asked them to inform us when they want to start work.”
Expansion joints are separations between two slabs of the deck and are meant to absorb the temperature-induced expansion and contraction of construction materials, and vibrations caused by earthquakes and soil subsidence. The joints are covered in rubber sockets to reduce corrosion.
Senior structural engineers at the port trust said the Howrah bridge has eight expansion joints and 10 “articulation joints” around the bridge’s bearings.
These joints around the bearings have 450 pads of various sizes and they help facilitate the movement of the bridge’s deck, the engineers said.
“Close to 20 per cent of the joints get damaged every year because of the huge traffic load and regular wear and tear,” said a senior official. “Almost every year, a specialised agency is entrusted to inspect the joints and the pads.”
The Howrah bridge, opened in 1943, is one of the busiest cantilever bridges of the world. It is used by close to 90,000 vehicles and 1.5 lakh pedestrians every day, senior port trust officials said.
The bridge has 78 hangers. The cantilever structure has been designed in such a way that the load gets transferred to the girders under the belly of the deck, from where the hangers shift the weight to the structure overhead.
Corrosion is one of the bigger challenges that the maintenance team faces.
“The replacement of expansion joints and pads is crucial because it helps keep the bridge’s deck surface traffic-worthy,” the official said.
Structural engineers said if the rubber of the expansion joints gets damaged, dust and debris tend to accumulate in the joints. Rainwater seepage is another threat and can potentially damage the steel girders under the deck and the bearings that support them.
If any or all of these things happen, the safety of the bridge is compromised, they said.
